The comment came after Fallon injured himself in October at a Harvard party - the third such incident in recent months.

'Something to worry about': Fallon's heavy drinking is said to be causing issues within his marriage, and also worrying bosses at NBC

He had been 'holding a bottle of Jägermeister' and greeting fans when he tripped over a woman who had bent down in front of him, People reported. He fell and landed on the broken glass.

The tumble follows a more serious injury in June, when the Tonight Show host had to be rushed to hospital after nearly severing a finger when he caught his wedding ring on a table corner during a freak fall at home.

He had been seen the evening before dining at Italian restaurant Scalinatella in the Upper East Side, sipping wine and posing for photos with fans.

The comedian was forced to undergo surgery to save his finger, and spent 10 days in intensive car, forcing The Tonight Show to go on a two-week hiatus.

Fallon then chipped his tooth while trying to tend to his injured finger eight weeks later.

In January, an inebriated Fallon was filmed drinking shots and singing at the West Village gay bar Marie's Crisis.

He even got on top of the piano at one point and sang 'Theme from Greatest American Hero (Believe It or Not)'.

One New York bartender told the New York Post she had served him numerous times over the years and remembered him partying late into the night.

'He's a mess,' she told the New York Post. 'Everything you've heard [about his behavior] is true.'

His friends seem to agree.

Last year, Fallon's former Saturday Night Live co-star, Horatio Sanz told New York magazine they had both been 'superfunctioning alcoholics' to blow off steam from the stresses of the job.

Yet, while NBC are becoming increasingly concerned about Fallon, according to insiders, no-one has yet intervened.

In fact, in August Fallon's contract was extended until 2021.

A network spokesman told the New York Post: 'Jimmy Fallon is a highly valued member of the NBC family who is both a tireless worker and an extraordinarily gifted performer.

'His dedication in putting on a great show each and every night is unparalleled, and that is reflected in the large amount of viewers who tune in — he frequently out-rates the broadcast competition combined. We are proud of his accomplishments on and off camera and look forward to working with him for many years to come.'